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Abstract

Accretion of extraterrestrial material to earth is of interest for a variety of
reasons, including as a possible driver of long or short-term climate change, and as a
record of solar system events preserved in the geological record. 3He is highly
enriched in extraterrestrial material, and provides a useful tracer of its input into
sedimentary archives. Previous work showed that polar ice could be a suitable archive
for studying variations in extraterrestrial input. Additional measurements reported here
confirm that the late Quaternary 3He flux derived from Antarctic ice samples is similar to
3He fluxes determined from marine sediments. The mean flux from nine replicate ~ 1
kg ice samples from the Vostok ice core site (112-115 m depth, age of ~ 3800 years) is
1.25 ± 0.37 x 10-12 cm3 STP cm-2 ka-1 (mean ± 2se). The large range for the 9 replicates
is probably due to the small number of interplanetary dust particles (IDPs) present, and
illustrates that large ice samples are required for precise constraints on temporal
variations in the 3He flux. Size fraction experiments show that the majority of the 3He
flux is delivered by particles in the 5-10 micron size range, consistent with the
hypothesis that helium in IDPs is primarily solar helium implanted in particle surfaces.